A solid catalyst component containing magnesium, titanium, an electron donor compound, and a halogen as essential components used for polymerization of olefins such as propylene has been known in the art. A large number of methods for polymerizing or copolymerizing olefins in the presence of a catalyst for olefin polymerization comprising the above solid catalyst component, an organoaluminum compound, and an organosilicon compound have been proposed. For example, Patent Document 1 (JP-A-57-63310) and Patent Document 2 (JP-A-57-63311) propose a method for polymerizing olefins with three or more carbon atoms, in which a catalyst comprising a combination of a magnesium compound, a titanium compound, and an organosilicon compound having an Si—O—C bond is used. However, because the method is not necessarily satisfactory for producing highly stereoregular polymers in a high yield, improvement of these methods has been desired.
Patent Document 3 (JP-A-63-3010) proposes a catalyst and a method for polymerizing propylene. The catalyst comprises a solid catalyst component, obtained by processing a powder produced from a dialkoxy magnesium, an aromatic dicarboxylic acid diester, an aromatic hydrocarbon, and a titanium halide with heat, an organoaluminum compound, and an organosilicon compound.
Patent Document 4 (JP-A-1-315406) proposes another catalyst for propylene polymerization and a method for polymerizing propylene in the presence of this catalyst. The catalyst for propylene polymerization comprises a solid catalyst component prepared by causing a suspension liquid containing diethoxymagnesium and an alkylbenzene to come in contact with titanium tetrachloride, reacting the suspension liquid with phthalic acid chloride, and causing the resulting solid product to come in contact with titanium tetrachloride in the presence of an alkylbenzene, an organoaluminum compound, and an organosilicon compound.
All of the above-described technologies have attained certain results in improving catalytic activity to the extent of permitting dispensing with an ash-removal step for removing catalyst residues such as chlorine and titanium from formed polymers, improving the yield of stereoregular polymers, and improving durability of catalytic activity during polymerization. However, there is a demand for continued improvement of such a catalyst.
The polymers produced using these catalysts are used in a variety of applications including formed products such as vehicles and household electric appliances, containers, and films. These products are manufactured by melting polymer powders produced by polymerization and, after palletizing, forming the polymer using various molds. In manufacturing formed products, particularly large products by injection molding, melted polymers are sometimes required to have a high fluidity (melt flow rate: MRF). In particular, for the purpose of cost reduction in the manufacture of a highly functional block copolymer to be used as a vehicle material, in a method of producing a copolymer in an amount just required for obtaining an olefin-based thermoplastic elastomer (hereinafter referred to as “TPO”) in a copolymerization reactor, and obtaining the TPO directly in the polymerization reactor without adding a separately produced copolymer, that is, in so-called “manufacture of a reactor-made TPO by direct polymerization”, a melt flow rate of 200 or more is demanded in a homopolymerization stage in order to produce a finished product with a high melt flow rate and to ensure ease of injection molding. For this reason, many studies for increasing the melt flow rate of polymers have been undertaken.
The melt flow rate greatly depends on the molecular weight of the polymers. In the industry, hydrogen is generally added as a molecular weight regulator for polymers during polymerization of propylene. In this instance, a large quantity of hydrogen is usually added to produce low molecular weight polymers having a high melt flow rate. However, the quantity of hydrogen which can be added is limited because pressure resistance of the reactor is limited for the sake of safety. In order to add a larger amount of hydrogen in vapor phase polymerization, the partial pressure of monomers to be polymerized has to be decreased, resulting in a decrease in productivity. The use of a large amount of hydrogen also brings about a problem of cost. As a method for solving this problem, Patent Document 5 (WO 2004-16662) proposes a method of producing a polymer having a high melt flow rate by using a compound shown by the formula Si(OR1)3(NR2R3) as a catalyst component for polymerization of olefins.
However, because these methods are not necessarily satisfactory for basically solving the above problems of TPO production by direct polymerization, improvement of these methods has been desired.    (Patent Document 1) JP-A-57-63310 (Claims)    (Patent Document 2) JP-A-57-63311 (Claims)    (Patent Document 3) JP-A-63-3010 (Claims)    (Patent Document 4) JP-A-1-315406 (Claims)    (Patent Document 5) WO 2004-16662 (Claims)
Therefore, an object of the present invention is to provide a catalyst component and a catalyst for polymerization of olefins capable of excellently maintaining stereoregularity and yield of a polymer and capable of producing olefin polymers having a high melt flow rate with a given amount of hydrogen (excellent hydrogen response), and a process for producing an olefin polymer using the catalyst component or the catalyst.